Pour cold water and lemon juice into an electric pressure cooker (such as Instant Pot(R)). Place a steamer rack inside; spray with cooking spray. Place frozen salmon fillets on the rack, skin-side down. Cover and close vent.
Set cooker to the Steam 2 setting; cook for 3 to 4 minutes. Release vent immediately when pot beeps.
Check salmon for desired doneness; fish should flake easily with a fork. Season with salt and pepper. Cover pot to keep salmon warm until serving.